The invention relates to a process for the carbonylation of acetylenically unsaturated compounds.
The invention is of particular interest for the preparation of esters of unsaturated carboxylic acids such as acrylic acid and methacrylic acid. It is well known that the alkyl esters of these acids, in particular the methyl and butyl esters, are of great commercial importance.
The general preparation of esters of unsaturated acids by carbonylation of acetylenically unsaturated compounds is known. In EP-186228, for example, a process for the carbonylation of acetylenically unsaturated compounds is described in which a catalyst system comprising a palladium compound, a phosphine and a protonic acid are used. The examples illustrate the use of, optionally substituted, hydrocarbylphosphines such as (substituted) triphenylphosphine. These phosphines are used in relatively large amounts, i.e. 5 to 500 moles per gramatom of palladium.
Another process for the carbonylation of acetylenically or olefinically unsaturated compounds is disclosed in EP 441.446. In this process, esters of unsaturated acids are prepared using a catalyst system which comprises a source of a Group VIII metal, a phosphine having an aromatic substituent which contains an imino nitrogen atom, a protonic acid and a tertiary amine. All examples relate to the use of catalyst systems containing palladium and a pyridylphosphine ligand.
Some in the art have investigated whether the carbonylation of unsaturated compounds is restricted to the use of palladium containing catalysts or whether satisfactory conversions and yields can be obtained with a catalyst comprised of a Group VIII metal other than palladium. GB 2202165 describes a process in which ethene, acrylic acid, or an acrylate ester is reacted with carbon monoxide in the presence of hydrogen, using a catalyst system formed by combining a platinum (II) compound, an organic ligand containing at least two phosphorus atoms coordinating with the platinum atom and a protonic acid having a pKa below 3. As unsaturated starting materials only ethene, acrylic acid and acrylic esters are mentioned. However, in this process the predominant reaction product is not an ester but a ketone.